The present invention relates to a flat display in which electrons emitted from an electron-emitting source are collided against phosphors to emit light.
In general, as a display device such as a FED (Field Emission Display) or a flat vacuum fluorescent display in which electrons emitted from an electron-emitting source serving as a cathode are collided against a light-emitting portion formed of phosphors on a counterelectrode to emit light, a flat panel display is available. In recent years, as a flat panel display of this type, various types that use nano tube fibers, e.g., carbon nano tubes or carbon nano fibers, as the electron-emitting source have been proposed.
A conventional flat display described in Japanese Patent Laid-Open No. 2002-343281 (reference 1) has a substrate 101 made of glass or the like and a front glass plate 103 which is at least partly transparent, as shown in FIG. 5. The substrate 101 and front glass plate 103 are arranged to oppose each other through a spacer glass frame (not shown) at a predetermined gap, and are adhered to the spacer glass frame with low-melting frit glass to form part of an envelope. The interior of the envelope is held at a vacuum degree on the order of 10−5 Pa. A gate electrode structure 120 is disposed in the envelope to be substantially parallel to the substrate 101 and front glass plate 103.
A plurality of substrate ribs 102 are formed on one surface of the substrate 101 to be parallel to each other at predetermined intervals. Band-like cathodes 110, to the surface of which nano tube fibers, e.g., carbon nano tubes or carbon nano fibers, are fixed as an electron-emitting source and which are made of a metal member such as a 426 alloy, are arranged in regions sandwiched by the substrate ribs 102 on the substrate 101, such that the cathodes 110 are leveled with the substrate ribs 102.
A plurality of thin plate-like front ribs 104 are formed at predetermined intervals on that surface of the front glass plate 103 which opposes the substrate 101, in a direction perpendicular to the substrate ribs 102 and cathodes 110. The end faces of the front ribs 104 which oppose the substrate 101 have thin, elongated rectangular shapes. A predetermined number of sets each including red-, green-, and blue-emitting phosphor screens 105R, 105G, and 105B in this order are arranged in those regions on the front glass plate 103 which are sandwiched by the front ribs 104. Metal-backed films 106 to serve as anodes are formed on those surfaces of the phosphor screens 105R, 105G, and 105B which oppose the glass substrate 101.
The front ribs 104 are formed by repeated printing, e.g., screen printing, on the front glass plate 103 until the front ribs 104 reach a predetermined height. Regarding the front ribs 104, a direction perpendicular to the main surface of the front glass plate 103 (the moving direction of electrons extracted from the cathodes 110 (to be described later)) will be referred to as “the direction of height”. The direction of the plate thickness of the front ribs 104 (the longitudinal direction of the substrate ribs 102) will be referred to as “the widthwise direction”, and a direction perpendicular to “the widthwise direction” and “the direction of height” (the longitudinal direction of gate electrodes 123 (to be described later)) will be referred to as “the lengthwise direction” hereinafter.
The gate electrode structure 120 disposed in the envelope is sandwiched between the end faces of the substrate ribs 102 on the substrate 101 and the end faces of the front ribs 104 of the front glass plate 103. The gate electrode structure 120 includes a glass plate 121 parallel to the substrate 101, a field control electrode 122 formed on the front glass plate 103 side surface of the glass plate 121, the band-like gate electrodes 123 formed on the substrate 101 side surface of the glass plate 121 to respectively correspond to the phosphor screens 105B, 105G, and 105R, and an insulating layer 124 formed on the substrate 101 side surface of the glass plate 121 to cover the gate electrodes 123. A plurality of electron-passing holes 125, through which the field control electrode 122, glass plate 121, gate electrodes 123, and insulating layer 124 communicate with each other in “the direction of height”, are formed in those regions of the gate electrode structure 120 where the gate electrodes 123 and cathodes 110 intersect.
The field control electrode 122 which is in contact with the front ribs 104 electrically shields the gate electrodes 123 and cathodes 110. A potential difference between the cathodes 110 and the metal-backed films 106 which serve as anode electrodes generates no electrical field in the region where the field control electrode 122 is formed. Thus, any damage due to electrical discharge to the electron-emitting source, particularly to the surface of the electron-emitting source, is prevented.
In the flat display with the above structure, a predetermined potential difference is supplied between the gate electrode structure 120 and cathodes 110 such that the gate electrode structure 120 side has a positive potential. Thus, electrons extracted from those regions of the cathodes 110 which intersect the gate electrodes 123 are emitted from the electron-passing holes 125. At this time, if a positive potential (acceleration potential) is applied to the metal-backed films 106, the electrons emitted from the electron-passing holes 125 are accelerated toward the metal-backed films 106, and collide against the phosphor screens 105B, 105G, and 105R through the metal-backed films 106 to emit light.
In the conventional flat display, the front ribs 104 formed on the front glass plate 103 cooperate with the substrate ribs 102 (and cathodes 110) formed on the substrate 101 to sandwich the gate electrode structure 120. The front ribs 104 also have the function of supporting the front glass plate 103, so the front glass plate 103 will not be broken by the pressure difference between the interior of the envelope and the outside, and the function of defining the distance between the metal-backed films 106 serving as the anodes and the field control electrode 122.
The front ribs 104 having the above functions are formed by repeating screen printing, as described above, so that, for example, they each have a width of 50 μm and that the distance between the gate electrodes 123 of the gate electrode structure 120 and the metal-backed films 106 is 2.0 mm to 4.0 mm.
To further improve the resolution of the conventional flat display as described above, the regions where the phosphor screens 105B, 105G, and 105R are arranged must be finer. For this purpose, it is indispensable to decrease the widths of the front ribs 104. As described above, however, of the shape of the end face of each front rib 104, the size in the widthwise direction is smaller than the size in the lengthwise direction. With the conventional method of repeating screen printing, to form narrower front ribs 104 at narrower pitches is limited. If the front ribs 104 are to be formed with narrower pitches, they cannot reach the predetermined height.
If the narrow-pitch front ribs 104 having a height smaller than in the conventional case are applied to a flat display, the gap between the anodes and field control electrode 122 becomes shorter than in the conventional case. When a high voltage of, e.g., about 10 keV is applied to the anodes, the field control electrode 122 cannot electrically shield the gate electrodes 123 sufficiently. Abnormal electrical discharge occurs between the anodes and gate electrodes 123 to damage the electron-emitting source.